Many devices are used for the cryotherapy of rheumatic diseases according to which the cold treatment gas is obtained by vaporizing liquid nitrogen. Air, which is mixed with the vaporized nitrogen, is used for heat exchange. Such devices, as for example, known from German patent publication Nos. 32 42 881 and 33 05 434, are suited for hospitals or therapy centers where a large number of treatment are planned.
These large devices require a quite high surveillance and safety expense. Thus, the oxygen content of the treatment room must be monitored since, in the case of sparse ventilation, it could drop to an unacceptable value. It must be assured that no air can condense in the storage vessel for liquid nitrogen. Concentrations of oxygen could hereby form in the liquid nitrogen from which (oxygen concentrations), after subsequent vaporization, explosive gas mixtures could result. Aside from this, effective installations for drying the air or the treatment gas are required since moisture which has frozen may not come in contact with the part of the body to be treated. These devices are therefore less suitable for normal medical practices where a treatment is only occasionally performed.